The invention relates to a toothing testing apparatus in which a disk or a ball (both sometimes hereinafter referred to as a "measuring ball" for the sake of simplicity) of a certain diameter is introducible into each of two tooth spaces lying roughly diametrically opposite each other in a testpiece having a toothing, and the distance of these two measuring balls from each other ("measure between or over two balls") is measured, wherein a measuring probe lies against each of the measuring balls, and wherein means are further provided with which the measuring ball in question is symmetrically positionable in the tooth space concerned. Measurement of the distances between the two flanks of a tooth space of a testpiece, particularly on the pitch circle of this toothing, is thus possible by conversion of the distances between the two measuring balls measured with such a tooth testing apparatus. Various apparatuses are known for this measurement, e.g. according to DE-PS 3109334. That arrangement does produce satisfactory measurement results. A drawback, however, is that it operates only mechanically and requires a relatively large amount of space, as probes in that arrangement extend virtually over the whole length of the testing apparatus.
DE-OS 4035302 discloses an internal toothing measuring device which operates with a mechanical deflection, but includes no guide toothing. Measurement requires a laborious actuation by hand, the measuring rollers having to be swivelled to and fro. DE-OS 3327549 discloses an automatic toothed-wheel testing apparatus in which two probes are used, each of which displays means in the form of an electrical, inductive measurement of the probe measurement path. Measuring balls lie in each case against a flank of neighbouring teeth, with which the pitch is measured. A "measure between or over two balls" is not measured.
Known from publications indicating Spline Gages (Series V) of the Applicant are internal and external toothing testing apparatuses in which the measuring probes do operate electrically, i.e., the detected "measure between or over two balls" is converted into electrical values. However, considerable space is required for such an apparatus and moreover, the apparatus is a relatively costly design.
Compared with the above, the task or problem posed for the invention is that of developing a testing apparatus in such a way that the "measure between or over two balls" can be measured with a much smaller space requirement than hitherto possible and which measurement can be converted into electrical values, and also in such a way that the symmetrical positioning in the toothing space concerned (so-called "floating") is achieved.